Mustang GT Boss 5.0L Block And Stroker Upgrade

Building Big With A Ford Racing Boss Block And A RGR/JPC Stroker Combination.

Michael Galimi

May 1, 2009

In 1996 Ford Motor Company transplanted its newest engine, the 4.6L modular motor, into the Mustang GT. Gone were the days of the famed and very popular 5.0L, which had a great run from the late '60s through the end of the Fox platform. The introduction of the mod motor had hardcore enthusiasts freaking out about the complex OHC design, the apparent lack of aftermarket components, and the intricate computer system controlling it all.

Thankfully, it wasn't long before aftermarket companies and enthusiasts stepped up and began unlocking the hidden horsepower. Complexity couldn't deter Mustang enthusiasts and soon the computer tuning was conquered, the voodoo of overhead camshaft design wore off, and making power was an easy thing to do thanks to power adders and then stroker kits. In 2005, Ford continued to revise the 4.6L mod motor and introduced the Three-Valve SOHC induction system on a similar short(er)-deck 4.6 mod motor.

The Three-Valve addressed many issues that Two-Valve mod motors lacked, which was a decent set of cylinder heads from the factory. SVT Mustang owners benefited from free-flowing and robust Four-Valve heads, but the base GT always suffered with the Two-Valve variant. Overall, variable camshaft timing, great cylinder heads and a high-flow intake helps the current mod motor crank out 300 hp and enables S197 Mustangs to run quickly on the track and street. The Three-Valve combo is certainly good, but is grossly underpowered when compared to the GM LS-series engines and modern Hemi competition.

We have seen people overcome the smallish cubes thanks to forced induction and various stroker engines, but the ability to build one bigger than 300ci has been rare. The mod motor simply isn't designed to handle a large bore due to the inherent design of the block. "Adding Darton sleeves allows a stock block to be opened up, but it gets costly with specialized machining needed for the sleeves," comments Rich Groh of Rich Groh Racing Engines.

The stroke has been generous and in stock trim it boasts a 3.542-inch throw, far longer than the 302's stock 3.00-inch crankshaft. The longer stroke has helped the 281ci mod motors excel in the torque department, but the narrow bore (3.552-inches) has been a major restriction in achieving big displacement.

Two years ago, Ford Racing Performance Parts released a new engine block that would allow for large bore sizes, not in the traditional pushrod small-block Ford sense, but big for the modular segment. Its name is the legendary Boss and the block was promptly run around the industry with the logo, "The Boss Is Back." Ford Racing released two versions, a 4.6L modular block and a pushrod unit (8.2-inch deck). Both blocks became an instant success.

On the modular front, it didn't take long for engine shops to shed the 298ci-302ci standard stroker sizes and go bigger. After all, bigger is better-right? The larger 3.70-inch bore allows engines to grow excessively and safely when compared to the stock block-based applications. The overall block strength increased dramatically over the factory blocks, including the popular Teksid unit.

One popular engine for stroked out maniacs has been the 322ci combination that is offered by JPC Racing and built by Rich Groh Racing Engines. The two shops have collaborated on using a Boss mod block and then combining it with a Paschal Performance 3.750-inch stroke crankshaft to come up with an LSX-slaying combination. This article focuses on a Three-Valve engine, but the short-block can be combined with any mod motor cylinder heads.